The present invention relates to a supporting apparatus for an objective lens used in an optical apparatus such as an optical scanner or the like or used in a data recording/reproducing apparatus which records/writes data with respect to an optical recording medium such as an optical disk drive, postscript type disk drive, phase change disk drive, CD-ROM, DVD, optical card, or the like, and also relates to a supporting apparatus for an optical element such as a galvano mirror or the like.
Conventionally, an optical element internally having a movable part or a movably supported optical element is used in various optical devices as described above. For example, in an optical element of an optical element such as a galvano mirror, an optical element such as an internal mirror or the like is supported to be rotatable and another optical element such as an objective lens which enables focus control is supported to be movable in a predetermined direction.
In many cases, a supporting apparatus based on a spring has been conventionally used as an apparatus for movably supporting an optical component or element of a small size. This type of supporting apparatus supports a movable part by a spring, and the movable part is supported to be freely rotatable about a predetermined axis or movable freely in a predetermined direction by deformation of the spring. An example of a conventional supporting apparatus of this type is disclosed in Japanese Patent Application KOKAI Publication No. 7-93783.
FIGS. 17 and 18 show a schematic structure of a conventional supporting apparatus such as a mirror supporting apparatus for a galvano mirror. In the figures, the reference 201 denotes a fixing member in a fixed side, which is formed by injection molding of a synthetic resin material or the like, for example. Further, a concave portion 203 is formed at the center portion of the fixing member 201, and a movable member 202 is supported on the concave portion 203 to be rotatable and movable, for example. Further, a mirror or the like (not shown) is attached to this movable member 202.
This supporting apparatus is provided with a spring 204 for supporting the movable member 202. This spring 204 is integrally formed from a thin plate material made of a spring material and comprises a frame-like fixed-side attachment portion 205 and a movable-side attachment portion 206. This movable-side attachment portion 206 is integrally connected by linear spring portions 207 having a narrow width. Further, the fixed-side attachment portion 205 described above is attached on the upper surface of a fixing member 201, for example, by screws or the like, and the movable member 202 is attached to the movable-side attachment portion 206.
The movable member 202 described above is supported to be rotatable by twisting deformation of the spring portions 207. In addition, since the spring portions 207 can be bent to be deformed, the movable member is also supported to be movable in the vertical direction.
The conventional supporting apparatus exemplified above has a drawback as follows. That is, preferably, the spring 204 described above has a small size as a whole and the spring portion 204 is also deformed with a spring coefficient which is as small as possible. It is therefore formed of a thin plate material. Consequently, the fixed-side attachment portion 205 and the like of this spring 204 can be easily deformed and are deformed by an external force caused by tightening the attachment screws or by thermal deformation of the fixing member 201 and the like. This deformation influences the spring constant of the spring portion 207 and affects the support precision and the support characteristic for the movable member 202.
In particular, the fixing member 201 described above is formed of a synthetic resin material so that the thermal expansion coefficient is relatively large. The spring 204 is formed of a metal material such as a beryllium-copper alloy or the like so that the thermal expansion coefficient is relatively small. Therefore, the fixed-side attachment portion 205 or the like made of a thin plate material is easily deformed due to a difference between the thermal expansion coeffeicients of both components, so that the precision of the galvano mirror is lowered.
In addition, the fixing member 201 is made of a synthetic resin material as described above, and the synthetic resin material generally has a small elastic coefficient. Therefore, the fixing member 201 is easily deformed by an external force such as tightening of screws during assembly, so that the deformation affects the support precision and the support characteristic of the fixing member 201. Therefore, the dimensions of respective parts of the fixing member must be enlarged so that the rigidity of respective parts is increased, in order to prevent undesired deformation of the fixing member 201. In this manner, a drawback appears in that the optical element such as a galvano mirror or the like has an enlarged size.